U.S. patent application number 13/000481 was filed with the patent office on 2011-05-12 for aluminium brazing sheet material.
This patent application is currently assigned to ALERIS ALUMINUM KOBLENZ GMBH. Invention is credited to Achim Burger, Theobald De Haan, Adrianus Jacobus Wittebrood.
Application Number | 20110111254 13/000481 |
Document ID | / |
Family ID | 40056207 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110111254 |
Kind Code |
A1 |
Wittebrood; Adrianus Jacobus ;
et al. |
May 12, 2011 |
ALUMINIUM BRAZING SHEET MATERIAL
Abstract
A brazing sheet material for CAB brazing without applying flux.
The brazing sheet material including an aluminum core alloy layer
provided with a first brazing clad layer material on one or both
sides of the aluminum core layer and at least one second brazing
clad layer material positioned between the aluminum core alloy
layer and the first braze clad layer material. The second brazing
clad layer material is an Al--Si alloy brazing material having 5%
to 20% Si and 0.01% to 3% Mg, and the first brazing clad layer
material is an Al--Si alloy brazing material having 2% to 14% Si
and less than 0.4% Mg. Also disclosed is a brazed assembly
manufactured in a brazing operation.
Inventors: |
Wittebrood; Adrianus Jacobus;
(Velserbroek, NL) ; De Haan; Theobald; (Uden,
NL) ; Burger; Achim; (Hohr Grenzhausen, DE) |
Assignee: |
ALERIS ALUMINUM KOBLENZ
GMBH
|
Family ID: |
40056207 |
Appl. No.: |
13/000481 |
Filed: |
June 25, 2009 |
PCT Filed: |
June 25, 2009 |
PCT NO: |
PCT/EP09/57956 |
371 Date: |
January 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61077615 |
Jul 2, 2008 |
|
|
|
Current U.S.
Class: |
428/654 ;
228/219; 228/221 |
Current CPC
Class: |
B23K 35/0222 20130101;
B23K 35/0238 20130101; B23K 35/002 20130101; B23K 35/0233 20130101;
C22C 21/04 20130101; Y10T 428/12764 20150115; B23K 35/286 20130101;
C22C 21/02 20130101; B23K 35/28 20130101 |
Class at
Publication: |
428/654 ;
228/219; 228/221 |
International
Class: |
B32B 15/01 20060101
B32B015/01; B32B 15/20 20060101 B32B015/20; B23K 1/00 20060101
B23K001/00; B23K 31/02 20060101 B23K031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2008 |
EP |
08012003.3 |
Claims
1. A brazing sheet material comprising of an aluminium core alloy
layer provided with a first brazing clad layer material on one or
both sides of said aluminium core layer and at least one second
brazing clad layer material positioned between the aluminium core
alloy layer and the first braze clad layer material, wherein the
second brazing clad layer material is an Al--Si alloy brazing
material having 5% to 20% Si and 0.01% to 3% Mg, and wherein the
first brazing clad layer material is an Al--Si alloy brazing
material having 2% to 14% Si and less than 0.4% Mg.
2. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material has a Mg content of less
than 0.15%.
3. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material is Mg-free.
4. Brazing sheet material according to claim 1, wherein the second
Al--Si alloy brazing clad layer material has a Mg content in a
range of 0.01% to 1%.
5. Brazing sheet material according to claim 1, wherein the sum of
the Mg content in the first and second Al--Si alloy brazing clad
layer material does not exceed 0.25%.
6. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material has a Si content in the
range of 4% to 14%.
7. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer has a composition within the range
of AA4045 or AA4343-series aluminium alloy.
8. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material has a Si content in the
range of 2.0% to 5%.
9. Brazing sheet material according to claim 1, wherein the second
Al--Si alloy brazing clad layer material further contains one or
more wetting elements, and wherein the total amount of the wetting
elements is in a range of 0.01% to 0.5%.
10. Brazing sheet material according to claim 1, wherein the second
Al--Si alloy brazing clad layer material furthers contains Bi as
wetting element in a range of 0.01% to 0.5%.
11. Brazing sheet material according to claim 10, wherein the
excess Mg with respect to the stoichiometric composition of
Bi.sub.2Mg.sub.3 is 0.07% or less.
12. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material further contains one or
more wetting elements, and wherein the total amount of the wetting
elements is in a range of 0.01% to 0.5%.
13. Brazing sheet material according to claim 1, wherein each of
the first and second Al--Si alloy brazing clad material layers may
further contain up to 0.8% Fe, and up to 0.2% Ti, and balance
unavoidable impurities and aluminium.
14. Brazing sheet material according to claim 1, wherein at least
one of the first and second Al--Si alloy brazing clad material
layers further contain one or more elements selected from the group
consisting of 0.1% to 8% of Zn, 0.01% to 1% of In, 0.01% to 1% of
Sn, and 0.01% to 1% of Ge.
15. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad material layer has a thickness which is
3% to 15% of the entire thickness of said aluminium alloy brazing
sheet product, and the second Al---Si alloy brazing clad material
layer has a thickness of 3% to 20% of the entire thickness of said
aluminium alloy brazing sheet product.
16. A method of manufacturing an assembly of brazed components,
comprising the steps of: a.) forming the components of which at
least one is made from an aluminium brazing sheet material
according to claim 1; b.) assembling the components into an
assembly; c.) brazing the assembly without applying flux in an
inert gas atmosphere at a brazing temperature for a period long
enough for melting and spreading of the filler material; d.)
cooling the brazed assembly.
17. A method of manufacturing an assembly of brazed components,
comprising the steps of: a.) forming the components of which at
least one is made from an aluminium brazing sheet material
according to claim 1; b.) assembling the components into an
assembly; c.) brazing the assembly without applying flux in a
vacuum atmosphere at a brazing temperature for a period long enough
for melting and spreading of the filler material; d.) cooling the
brazed assembly.
18. A brazed assembly of components incorporating an aluminium
alloy brazing sheet according to claim 1.
19. A brazed assembly according to claim 18, wherein the brazed
assembly is an oil cooler or a B-tube.
20. Brazing sheet material according to claim 1, wherein the second
Al--Si alloy brazing clad layer material has a Mg content in a
range of 0.01% 0.50%.
21. Brazing sheet material according to claim 1, wherein the sum of
the Mg content in the first and second Al--Si alloy brazing clad
layer material does not exceed 0.10%.
22. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material has a Si content in the
range of 6% to 12%.
23. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material has a Si content in the
range of 2.0% to 4.0%.
24. Brazing sheet material according to claim 1, wherein the second
Al--Si alloy brazing clad layer material further contains one or
more wetting elements selected from the group consisting of Bi, Pb,
Li, Sb, Se, Y, and Th, and wherein the total amount of the wetting
elements in the second Al--Si alloy brazing clad layer material is
in a range of 0.01% to 0.5%.
25. Brazing sheet material according to claim 1, wherein the second
Al--Si alloy brazing clad layer material furthers contains Bi as
wetting element in a range of 0.01% to 0.25%.
26. Brazing sheet material according to claim 25, wherein the
excess Mg with respect to the stoichiometric composition of
Bi.sub.2Mg.sub.3 is 0.05% or less.
27. Brazing sheet material according to claim 1, wherein the first
Al--Si alloy brazing clad layer material further contains one or
more wetting elements selected from the group consisting of Bi, Pb,
Li, Sb, Se, Y, and Th, and wherein the total amount of the wetting
elements the first Al--Si alloy brazing clad layer material is in a
range of 0.01% to 0.5%.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a brazing sheet material comprising
of an aluminium core alloy layer provided with a first Al--Si alloy
brazing clad layer material on one or both sides of said aluminium
core layer and at least one second Al--Si alloy brazing clad layer
material positioned between the aluminium core alloy layer and the
first brazing clad layer material.
[0002] The invention further relates to a brazed assembly
manufactured in a brazing operation, the brazed assembly comprising
various components and at least one component being made from the
aluminium alloy brazing sheet according to this invention.
BACKGROUND TO THE INVENTION
[0003] As will be appreciated herein below, except as otherwise
indicated, aluminium alloy designations and temper designations
refer to the Aluminum Association designations in Aluminum
Standards and Data and the Registration Records, as published by
the Aluminum Association in 2008.
[0004] For any description of alloy compositions or preferred alloy
compositions, all references to percentages are by weight percent
unless otherwise indicated.
[0005] Substrates of aluminium or aluminium alloy in the form of
sheet or extrusion, are used to make shaped, or formed, products.
In some of these processes parts of (shaped) aluminium comprising
substrates are interconnected. One end of a substrate may be
interconnected with the other end, or one substrate may be
assembled with one or more other substrates. This is commonly done
by brazing. In a brazing process, a brazing filler metal or brazing
alloy, or a composition producing a brazing alloy upon heating, is
applied to at least one portion of the substrate to be brazed.
After the substrate parts are assembled, they are heated until the
brazing metal or brazing alloy melts. The melting point of the
brazing material is lower than the melting point of the aluminium
substrate or aluminium core sheet.
[0006] Brazing sheet products find wide applications in heat
exchangers and other similar equipment. Conventional brazing
products have a core of rolled sheet, typically, but not
exclusively an aluminium alloy of the 3xxx-series, having on at
least one surface of the core sheet an aluminium clad layer (also
known as an aluminium cladding layer). The aluminium clad layer is
made of an 4xxx-series alloy comprising silicon in an amount in the
range of 2 to 20% by weight, and preferably in the range of about 7
to 14% by weight. The aluminium clad layer may be coupled or bonded
to the core alloy in various ways known in the art, for example by
means of roll bonding, cladding spray-forming or semi-continuous or
continuous casting processes. These aluminium clad layers have a
liquidus temperature typically in the range of about 540 to
615.degree. C.
[0007] There are various brazing processes in use for the
industrial scale manufacturing of brazed assemblies such as heat
exchangers.
[0008] There is vacuum brazing ("VB") which is carried out at
relatively low atmosphere pressure in the order of about
1.10.sup.-5 mbar or less. To obtain the optimum conditions for
joining to take place, Al--Si brazing alloys commonly used for
vacuum brazing contain purposive additions of Mg of 1% or more. The
believed mechanism is that Mg destroys the hard oxide film of the
filler alloy when it evaporates from the brazing sheet during
brazing, and further the evaporated Mg plays the role as getter
that removes oxygen and moisture remaining in the brazing
furnace.
[0009] Such a Mg-containing brazing sheet product for vacuum
brazing is disclosed in U.S. Pat. No. 4,489,140 wherein the brazing
sheet product for vacuum comprising of a AA3000-series core alloy,
clad with a AA4104 brazing alloy layer and having an AA4343 brazing
alloy interposed between the core alloy and the AA4104 brazing
alloy layer to provide consistently good bonding between the core
and the AA4104 alloy. It is well known in the art that AA4104
alloys contain Mg in a range of 1.2 to 2.0% and Bi in a range of
0.02 to 0.2%, and that the AA4343 alloys have neither Bi nor
Mg.
[0010] U.S. Pat. No. 5,069,980 discloses a vacuum-brazing aluminium
cladding material consisting of a core member of aluminium alloy,
and a first clad and a second clad, said first clad consisting
essentially of 6 to 14% of Si, 0 to 0.6% Mg, and the balance being
Al, and said second clad consisting of 0 to 14% Si, and preferably
zero % Si, and 0.8 to 2.5% Mg and the balance being Al, and wherein
the thickness of the second clad is a function of the Si-content in
this second clad layer.
[0011] U.S. Pat. No. 4,161,553 discloses a brazing sheet product
for vacuum brazing, the brazing sheet comprising an aluminium alloy
core alloy, a first layer of an aluminium brazing alloy consisting
essentially of 0 to 2.5% Mg, 5.0 to 13.0% Si, max. 0.8% Fe, max.
0.3% Cu, max. 0.3% Zn, max. 0.3% Mn, balance aluminium, and a
second layer of an aluminium alloy clad on the first layer, said
second layer consisting essentially of 0.5 to 1.2% Mg, 1.2 to 1.8%
Si, max. 0.3% Cu, max. 0.7% Fe, max. 1.5% Mn, balance aluminium,
the second layer having a melting point substantially equivalent to
the melting point of the first layer. In an example each of the
first and second layer the aluminium alloys had a Mg content of
0.5%.
[0012] Another brazing process is controlled atmosphere brazing
("CAB") which is carried out in a dry no oxygen containing
atmosphere, preferably using the inert environment of nitrogen, but
for example also argon can be used. To facilitate brazing a
non-corrosive brazing flux, e.g. a fluoride based flux, is applied
prior to brazing on the pieces to be joined. This brazing flux
removes or at least brakes open during the brazing operation the
always present oxide layer to allow the molten filler to come into
contact with bare metal to form the joint. The aluminium alloys
used for CAB should be free of Mg because any Mg is inhibiting the
brazing flux action in removing the oxide layer. In complex shaped
assemblies the application of the non-corrosive brazing flux prior
to brazing at the interior of the assemblies is often considered
very difficult and problematic.
[0013] Yet another brazing process is CAB without using a brazing
flux, and this process is in particular being used for joining by
means of brazing of surfaces inside a heat exchanger with are very
difficult to flux and on an industrial scale is more cost effective
than a vacuum brazing operation as vacuum brazing requires
considerable capital equipment costs.
[0014] In European patent document EP-1430988-A1 it is disclosed
that for such a process of CAB without using a brazing flux that
the brazing sheet product used contains Mg at least in a layer
constituting the brazing sheet other than the filler alloy layer,
typically the core alloy contains Mg in a range of 0.05 to 1.0
wt.%. Interposed between the core alloy and the filler alloy an
diffusion prevention layer is present, such an a Mg-free
AA3003-series aluminium alloy.
[0015] European patent document EP-1306207-B1 discloses another
fluxless brazing process in an inert gas atmosphere containing a
very low oxygen content of up to 1000 ppm, and preferably up to 500
ppm. Furthermore there is disclosed a brazing sheet product
comprising of an aluminium core alloy on one or both sides clad
with an Al--Si alloy brazing alloy containing 0.1 to 5% of Mg and
0.01 to 0.5% of Bi as an intermediate layer, and a thin covering
material clad onto the Al--Si alloy brazing alloy. It is disclosed
that during a brazing operation the brazing material in the
intermediate layer is molten as the temperature is elevated during
brazing, but oxidation of the surface of the brazing material does
not occur because the surface is covered with the thin covering
material which remains solid. When the temperature is further
elevated, the portions with lower melting points, such as a
segregation portion of the thin covering material close to the
molten brazing material, are locally molten, and then the brazing
material seeps and spreads over the surface of the thin covering
material due to volumetric expansion. The surface of the brazing
material then becomes an emerging face without an oxidation film,
and new intensive oxidation does not proceed due to the inert gas
atmosphere.
[0016] There is a need for further improved brazing sheet materials
and brazing processes in which the interior side of an assembly
does not have to be provided with a brazing flux.
DECSRIPTION OF THE INVENTION
[0017] It is an object of the invention to provide an alternative
aluminium alloy brazing sheet material that can be applied in a
controlled atmosphere fluxless brazing process without applying a
brazing flux.
[0018] It is another object of the invention to provide an
aluminium alloy brazing sheet material that can be applied in a
controlled atmosphere fluxless brazing process without applying a
brazing flux as well as in a controlled atmosphere brazing process
with a brazing flux.
[0019] It is another object of the invention to provide an
aluminium alloy brazing sheet material that can be applied in a
controlled atmosphere fluxless brazing process as well as in a
controlled atmosphere brazing process with a brazing flux, as well
as in a vacuum brazing process.
[0020] These and other objects and further advantages are met or
exceeded by the present invention providing a brazing sheet
material comprising of an aluminium core alloy layer having a first
brazing clad layer material on one or both sides of said aluminium
core layer and at least one second brazing clad layer material
positioned between the aluminium core alloy layer and the first
braze clad layer material, wherein the second brazing clad layer
material is an Al--Si alloy clad brazing material having 5% to 20%
Si and 0.01% to 3% Mg, and wherein the first brazing clad layer
material is an Al--Si alloy brazing material having 2% to 14% Si
and less than 0.4% Mg.
[0021] In accordance with the invention it has been found that by
maintaining a very low Mg level in the first Al--Si alloy brazing
clad layer material and having a controlled purposive addition of
Mg to the second Al--Si alloy brazing clad layer material, a
brazing sheet product is provided that can be applied successfully
in a controlled atmosphere brazing process without the use of a
brazing flux.
In European patent document EP-1306207-B1 it is reported that in
order to achieve successful CAB brazing without the use of a
brazing flux it is required that both the top layer and the
aluminium core material layer should have a solidus temperature
higher than the liquidus temperature of the intermediate brazing
material layer. In this way the molten brazing material during a
subsequent brazing operation at a temperature between the liquidus
temperature and the solidus temperature is to cause the Al--Si
alloy brazing material layer to melt down while keeping the thin
covering material layer solid to prevent oxidation of the brazing
material being melted, and then cause the Al--Si alloy brazing
material to, due to volumetric expansion, seep through segregation
portions of the thin covering material layer onto a surface of the
thin covering material layer and spread over the surface of the
thin covering material to form an emerging surface resulting in a
brazed joint. Whereas in the brazing sheet material according to
the present invention the first and second Al--Si alloy brazing
clad layers may have substantially equivalent solidus and liquidus
temperatures, while still being able to be used successfully in a
controlled atmosphere brazing operation.
[0022] Furthermore, it has been found in accordance with this
invention that the brazing sheet product can be applied
successfully in a vacuum brazing operation despite the low level of
Mg in the filler metal formed by the first and second Al--Si alloy
brazing clad materials, more in particular where the first Al--Si
alloy clad material layer, being the outer clad layer, has a very
low Mg-content. This is contrary to industry practice for vacuum
brazing where the clad layer or outer lad layer material has a
typical Mg content of more than 1%.
[0023] In addition it has been found that the brazing sheet
material according to this invention is a very attractive candidate
for application in brazed assemblies having one or more inner
surfaces which are difficult to flux. Surprisingly, it has been
found, despite the use of Mg additions which are normally not
desirable for the flux brazing processes such as NOCOLOK
(registered trademark of Alcan), that the brazing sheet product
according to this invention can be brazed in a controlled
atmosphere brazing process while applying a brazing flux. This
makes the brazing sheet product a very attractive candidate for the
production of for example brazed oil coolers. Oil coolers are
commonly built up from plates which have to braze internally and
externally. Due to the long brazing cycle it is necessary to flux
the outside of the oil cooler to facilitate brazing. Long brazing
cycles would give otherwise excessive oxidation even in a
controlled atmosphere environment, thereby reducing the capability
to form reliable joints. The applied brazing flux reduces
significantly the degree of oxidation. Also, with the brazing sheet
product according to this invention good brazed joint are obtained
at inner surfaces without the requirement of applying a brazing
flux.
[0024] In the brazing sheet material according to the invention the
core alloy layer is made for an aluminium alloy. The core alloys
are preferably from the 2xxx-, 3xxx-, 5xxx-, or 6xxx-series
aluminium alloys, for example an AA3003, AA3005, AA6060 or
AA6063-type alloy.
[0025] When used in a CAB operation incorporating also the use of a
brazing flux it is preferred that the Mg-content in the core alloy
layer is being controlled such that it is not more than about 0.3%,
and more preferably not more than about 0.2%, and more preferably
not more than about 0.10%.
[0026] In an embodiment the core alloy layer is an AA3000-series
alloy having not more than about 0.3% Mg, in particular when used
to manufacture an article joined by means of CAB with applying a
brazing flux. More preferably the core alloy layer is an aluminium
alloy comprising, in wt. %:
TABLE-US-00001 Mn 0.5 to 2.0 Cu 0 to 1.2 Fe 0 to 1.0 Si 0 to 1.0 Bi
0 to 0.1 Ti 0 to 0.1 Mg 0 to 0.3, preferably 0 to 0.2,
[0027] other elements and inevitable impurities, each <0.05,
total <0.2, balance aluminium.
[0028] According to this invention the first Al--Si alloy brazing
clad layer comprises at least Si in a range of 2.0 to 14% and has
Mg, if present, of less than 0.4%.
[0029] In accordance with the invention it has been found that the
Mg content in the first Al--Si alloy brazing clad layer should be
kept low, and should more preferably be less than about 0.15%. On a
more preferred basis it is an Al--Si brazing alloy being Mg-free to
avoid the formation of an oxide layer during a brazing operation.
In practical terms this would mean that Mg is present at a very low
level of an impurity or incidental element, typically <0.08%,
and ideally at a level of <0.05%, and more preferably <0.01%.
More preferably the aluminium alloy is substantially free of Mg.
With "substantially free" is meant that no purposeful addition of
Mg was made to the chemical composition but that due to impurities
and/or leaking from contact with manufacturing equipment, trace
quantities of Mg may nevertheless find their way into the aluminium
alloy product.
[0030] In an embodiment of the first Al--Si alloy brazing clad
layer the Si content is preferably in a range of 2.0 to 5%, and
preferably in a range of 2.0 to 4.0%. In this embodiment there is a
significant difference in Si-content between the first and the
second Al--Si alloy brazing clad layer, which is of assistance in
the quality control of the clad liner thickness. A lower Si content
in the outer clad layer of the brazing sheet material results in a
lower die wear when shaping the brazing sheet material, for example
by means of bending or folding.
[0031] In another embodiment of the first Al--Si alloy brazing clad
layer the Si content is preferably in a range of about 4% to 14%,
and more preferably in the range of about 6% to 12%.
In an embodiment the first brazing clad material layer has a
chemical composition within the range of an AA4045 or an
AA4343-series aluminium alloy, preferably with the further proviso
that the alloy has a very low Mg content as set out in this
description, and ideally is Mg-free.
[0032] The second Al--Si alloy brazing clad material comprises Si
in a range of 5% to 20% and Mg in a range of 0.01% to about 3%. In
a preferred embodiment the lower-limit for the Si content is about
6%, and a preferred upper-limit for the Si content is about 14%. In
a preferred embodiment the Mg content has an upper-limit of about
1.5%.
[0033] In the embodiment where the brazing sheet material according
to this is applied in a CAB operation without the use of a brazing
flux, the Mg content in the second Al--Si alloy brazing material is
controlled in a range of 0.01% to about 1%, and more preferably the
upper limit is about 0.50%, and more preferably about 0.20%.
[0034] When used in a CAB operation, with or without the use of a
brazing flux, it is preferred that the sum of the Mg content in the
first and second Al--Si alloy brazing clad layers is controlled
such that it does not exceed about 0.25%, and preferably does not
exceed 0.10%. At present the quality and control mechanisms when
producing aluminium brazing sheet products allow for the target and
the control of Mg within an accuracy of .+-.0.01% or better.
[0035] Ideally, the Si content in the first and second Al--Si alloy
brazing material layer is selected such that the sum of the Si
contents of both layers is in a range of 6% to 12.5%, and
preferably in the range of 6% to 11%. In a more preferred
embodiment the sum of the Si content is in a range of 9% to 11%.
And in another preferred embodiment the sum of the Si content is in
the range of 6.5% to 8.5%.
[0036] The amount of Fe present in the Al--Si alloy brazing
material, both for the first and second Al--Si alloy brazing clad
material, depends primarily on the origin of the alloy material and
can be up to about 0.8%, and preferably is not more than about
0.6%. As grain refiner element Ti can be present in the brazing
material in a range of up to about 0.2%, preferably up to 0.15%.
The balance is made by unavoidable impurities and aluminium. Also
Cu can be present as a tolerable impurity element, typically to a
level of up to 0.3%, but preferably does not exceed 0.1%.
[0037] In an embodiment Mn can be present in the first and/or in
the second Al--Si alloy brazing material layer in the range of
about 0.2% to 0.8% to improve on the corrosion resistance of the
aluminium brazing sheet material. At a level below about 0.2% the
effect of improved corrosion resistance by the Mn addition is not
found. Preferably the amount of Mn is at least about 0.3% to
provide improved corrosion resistance. With a view to the
properties of the alloy, the amount of Mn should be not more than
1.0%, and a preferred maximum is 0.8%, since above this level the
improved corrosion resistance may be less. In the embodiment where
Mn is purposively added it is preferred that the Mn/Fe ratio in
weight percent is at least 1, and more preferably at least 2.
[0038] In the embodiment where Mn is purposively added to one or
both of the Al--Si alloy brazing materials layers, it is preferred
to have a difference in Mn levels between the two adjacent brazing
clad materials of at least about 0.1%, and preferably of at least
about 0.2%. A difference in Mn levels is of assistance as a quality
control means for the clad liner thickness, e,g. by means of
etching techniques. During a brazing operation the two Al--Si alloy
brazing materials form one filler metal to form a joint and
levelling out any compositional difference present prior to
brazing.
[0039] In an embodiment each of the first or second Al--Si alloy
brazing clad material layers further contains one or more wetting
elements. Preferably the wetting elements are selected from the
group comprising Bi, Pb, Li, Sb, Se, Y, and Th, and wherein the
total amount of the wetting elements is in a range of about 0.01%
to 0.5%. In a preferred embodiment the element Bi is selected from
the group of wetting elements and is in a range of about 0.01% to
0.5%, and preferably in a range of about 0.01% to 0.25%, as being
the most efficient wetting element for this purpose in this alloy
system during a brazing operation.
[0040] Preferably the wetting agent is added to the second Al--Si
alloy brazing material layer. In the embodiment that Bi is added to
the brazing material layer it is further preferred that excess Mg
content with respect to stoichiometric composition of
Bi.sub.2Mg.sub.3 is 0.07% or less, and preferably 0.05% or less. It
has been found that Bi has a low solubility in aluminium and tends
to separate out at the grain boundaries even when added at low
levels of for example about 0.1%. To overcome this a small amount
of Mg will form Bi.sub.2Mg.sub.3 which stops separation at the
grain boundaries. This Bi.sub.2Mg.sub.3 phase will however dissolve
in the Al--Si clad layer material at melting of the brazing
material releasing the Bi to lower the surface tension of the
molten filler.
[0041] In an embodiment each of the Al--Si alloy brazing clad
material layers may further contains one or more elements selected
from the group consisting of about 0.1% to 8% of Zn, about 0.01% to
1% of In, about 0.01% to 1% of Sn, and about 0.01% to 1% of Ge.
These alloying elements improve the corrosion resistance of the
core material by making the Al--Si brazing material more
sacrificial with respect to the core material. When the amount is
less than the lower limit the sacrificial anode effect is not
sufficient to produce the sacrificial anode effect, and when more
than the upper limit is present it does not provide any further
improvement on the corrosion resistance, whereas the alloy is more
difficult to manufacture.
[0042] There are several possible configurations for the brazing
sheet material according to the invention.
[0043] In an embodiment the core alloy layer is provided on one
side with the first Al--Si alloy brazing clad material layer and
with the second Al--Si alloy brazing clad material positioned
between the core alloy layer and said Al--Si alloy brazing clad
material, and whereby the other side of the core layer is bare such
that the brazing sheet material comprises of a three layer
configuration.
[0044] In an alternative embodiment of the brazing sheet material
according to this invention the core alloy layer is provided on
both sides with the first Al--Si alloy brazing clad material layer
and with the second Al--Si alloy brazing clad material positioned
between the core alloy layer and the first Al--Si alloy brazing
clad material. When both sides of the core layer are clad in the
same manner, the brazing sheet material comprises of at least a
five layer configuration.
[0045] In another embodiment, when one side of the core alloy layer
is clad with the two Al--Si alloys brazing clad material layers
according to this invention, on the other side of the core alloy
layer an outerlayer can be applied. The outerlayer or outerliner
would generally be of an alloy tailored to provide high corrosion
resistance or even corrosion combined with erosion resistance in
the environment to which that face of the brazing sheet material is
exposed, for example when used as a waterside liner in a heat
exchanger. An example of a suitable outerliner would be an
aluminium alloy having a purposive addition of Zn (up to about 6%),
such as for example an AA7072-series alloy.
[0046] In yet another embodiment a further aluminium alloy layer
can be interposed between the core alloy layer and the second
Al--Si alloy brazing clad material. For example a further aluminium
alloy layer may be applied for example to limit diffusion of
alloying elements from the core layer to the brazing layer or to
further improve on the corrosion performance of the brazing sheet
product.
[0047] The brazing sheet material according to this invention can
be manufactured via various techniques. For example by roll bonding
as is well known in the art. Alternatively one or more of the
Al--Si brazing alloy layers can be applied on the core alloy layer
by means of thermal spraying techniques. Or alternatively the core
alloy layer and the second Al--Si alloy braze clad material can be
manufactured by means of casting techniques, for example as
disclosed in international patent document WO-2004/112992, where
after the first Al--Si alloy braze clad material can be applied by
means of for example roll bonding or thermal spraying
techniques.
[0048] The brazing sheet material according to the invention has a
typical thickness at final gauge in the range of about 0.05 to 4
mm. The brazing sheet material is preferably up to about 350
microns thick at final gauge, and more preferably about 100 to
about 250 microns thick.
[0049] The first Al--Si alloy braze clad material layer has
preferably a thickness which is about 3 to 15% of the entire
thickness of aluminium alloy brazing sheet material. The second
Al--Si alloy braze clad material layer has a thickness of about 3
to 20%, and preferably about 3 to 15%, of the entire thickness of
the aluminium alloy brazing sheet material. The first and second
Al--Si alloy braze clad material layers may have about equal
thicknesses.
[0050] Preferably the sum of the thickness of the first and second
Al--Si alloy braze clad material layers applied on a side of the
core alloy layer are in a range of 5 to 20% of the entire thickness
of the aluminium alloy brazing sheet material.
[0051] In a further aspect of the invention there is provided an
article comprising at least two formed members joint by brazing,
for example a heat-exchanger, incorporating at least the aluminium
alloy brazing material according to this invention as one of the
formed members. A typical example of a heat-exchanger benefiting
for the aluminium alloy brazing material according to this
invention is an oil cooler, and whereby ideally at least the first
and second Al--Si alloy braze clad materials joints a hollow formed
in the article. Another typical example is a B-tube, its
configurations being well known to the skilled person, in which
there is an inner surface which cannot be fluxed whereas on the
outer surface fins should be joined to the tube.
[0052] In another aspect of the invention there is provided a
method of manufacturing an article joined by brazing or an assembly
of brazed components, comprising the steps of:
[0053] (i) forming the components of which at least one is made
from an aluminium alloy brazing material according to this
invention as set out above and the claims;
[0054] (ii) assembling the components into an assembly;
[0055] (iii) brazing the assembly without applying flux in an inert
gas atmosphere at a brazing temperature for a period long enough
for melting and spreading of the filler material; Typically the
oxygen content in the brazing atmosphere should be as low as
reasonable possible, and is preferably below 1000 ppm, and more
preferably below 200 ppm;
[0056] (iv) cooling the brazed assembly, typically to below
100.degree. C.
[0057] Ideally, when assembling the components into an assembly
suitable for joining by brazing, one side of the brazing sheet
material of the invention having the first and second Al--Si alloy
brazing clad material layers is being kept inside the assembly
forming the brazing sheet material to constitute a hollow
structure. While using the brazing sheet material according to this
invention there is no need to apply a flux in order to obtain a
good joint with the brazing operation.
[0058] In another aspect of the invention there is provided a
method of manufacturing an article joined by brazing or an assembly
of brazed components, comprising the steps of:
[0059] (a) forming the components of which at least one is made
from an aluminium alloy brazing material according to this
invention;
[0060] (b) assembling the components into an assembly, and wherein
one side of the brazing sheet material having the first and second
Al--Si alloy brazing material layer is being kept inside the
assembly formed by the brazing sheet material to constitute a
hollow structure;
[0061] (c) brazing the assembly without applying flux in the hollow
structure and applying a flux on at least part of the outside of
the assembly of components and brazing the whole assembly in an
inert gas atmosphere at a brazing temperature for a period long
enough for melting and spreading of the filler material; Typically
the oxygen content in the brazing atmosphere should be as low as
reasonable possible, and is preferably below 1000 ppm, and more
preferably below 200 ppm;
[0062] (d) cooling the brazed assembly, typically to below
100.degree. C.
[0063] In another aspect of the invention there is provided a
method of manufacturing an article joined by brazing or an assembly
of brazed components, comprising the steps of:
[0064] (a) forming the components of which at least one is made
from an aluminium alloy brazing material according to this
invention;
[0065] (b) assembling the components into an assembly;
[0066] (c) brazing the assembly without applying flux in a vacuum
atmosphere at a brazing temperature for a period long enough for
melting and spreading of the filler material;
[0067] (d) cooling the brazed assembly, typically to below
100.degree. C.
[0068] It has been found that the brazing sheet material according
to this invention can be brazed successfully in a vacuum brazing
operation. A good fillet formation is being obtained at
significantly lower Mg contents in the Al--Si brazing material
commonly used in vacuum brazing operations. Furthermore it has been
found that already a good fillet formation can be obtained at less
deep vacuum pressures than commonly applied in industrial scale
vacuum furnaces.
[0069] In the following, the invention will be explained by the
following non-limitative examples.
EXAMPLES
Example 1
[0070] In a series of experiments 1 mm brazing sheet material has
been manufactured. Core sheet of 45 mm has been produced from small
ingots which have been pre-heated at 430.degree. C. and then hot
rolled to 45 mm. Al--Si alloy clad materials to form the first and
the second clad layer has been produced from small ingots which
have been pre-heated to 430.degree. C. and hot rolled to 5 mm and
then cold rolled to 4 mm.
[0071] A five-layer brazing sheet product has been manufactured
consisted of a core alloy having a composition of 0.25% Fe, 0.1%
Si, 0.2% Mg, 0.5% Cu, 1.0% Mn, balance aluminium and impurities, on
both sides clad with a first Al--Si alloy brazing clad, and on both
sides of the core layer a second Al--Si alloy brazing material has
been positioned between the core alloy layer and the first brazing
clad layer. The composition of the first Al--Si clad material layer
was an AA4343-series alloy having 7.5% Si and being devoid of Mg.
The composition of the second Al--Si clad layer material was 12.7%
Si, 0.3% Fe, 0.09% Bi, 0.08% Mg, balance aluminium and
impurities.
[0072] This five-layer brazing sheet material has been manufactured
by placing on a 45 mm core sheet the various 4 mm clad layers. The
61 mm thick product was then for 3 hours pre-heated at 430.degree.
C., then hot rolled to 3 mm and then cold rolled to 1 mm. The 1 mm
brazing sheet material was annealed for 2 hours at 350.degree. C.
and thereafter the brazeability was assessed. Thus on each side of
the core layer two Al--Si brazing material layers are applied. The
thickness of each layer of the Al--Si alloy brazing clad material
was each about 5% of the total thickness of the brazing sheet
material.
[0073] The brazeability of the brazing sheet products have been
assessed on a laboratory scale of testing in a small quartz
furnace. Small coupons of 25 mm.times.25 mm were cut from the
brazing sheet products. A small strip of an AA3003 alloy measuring
30 mm.times.7 mm.times.1 mm was bent in the centre to an angle of
45.degree. and laid on the coupons. The strip-on-coupon samples
were heated under flowing nitrogen, with heating from room
temperature to 590.degree. C., dwell time at 590.degree. C. for 1
minute, cooling from 590.degree. C. to room temperature. The brazed
samples were assessed for the amount of fillet formed at the
periphery of the AA3003 in contact with the brazing sheet products
and expressed in %, for example if no fillet was formed then the
amount of fillet is 0%, and when a fillet is formed around the
whole periphery the amount of fillet is 100%.
[0074] It has been found that a 100% fillet formation was obtained
with the brazing sheet product according to this invention.
[0075] In a further brazing test the brazing sheet material has
been brazed in a industrial scale vacuum environment at about
595.degree. C. A similar fillet formation has been found as for the
CAB brazing cycle.
[0076] Thus, the brazing sheet product according to this invention
can be successfully brazed in both a CAB and a VB environment. VB
has been achieved at significantly lower Mg levels in the brazing
sheet product resulting in a lower Mg emission and consequently
increased the maintenance interval of the vacuum furnace.
Example 2
[0077] The five-layer brazing sheet material of Example 1 has been
shaped and applied in an assembly of components forming an oil
cooler. This oil cooler was built up from plates which have to
braze both internally and also externally. Due to the long brazing
cycle it was necessary to flux the outside of the oil cooler to
facilitate brazing by avoiding excessive oxidation, whereas the
inner surfaces of the oil cooler had not been fluxed. The oil
coolers had been brazed in an industrial scale controlled
atmosphere brazing furnace.
[0078] From observations it became clear that the non-fluxed inner
surfaces as well as the fluxed outside surfaces showed nice round
fillets which will provide amongst others a better fatigue
resistance.
Example 3
[0079] Using similar manufacturing conditions as set out in Example
1 above for comparison, a 1 mm brazing sheet product has been
manufactured consisting of a core layer clad on both sides with an
Al--Si alloy clad layer. The core alloy layer had a composition of
0.25% Fe, 0.1% Si, 0.2% Mg, 0.5% Cu, 1.0% Mn, balance aluminium and
impurities, and the clad layer had a composition of 12.7% Si and
0.3% Fe, balance aluminium and impurities.
[0080] It had been assessed for brazeability under similar CAB
brazing condition as for the 5-layer brazing sheet material of
Example 1, and it has been found that no fillet formation
occurred.
[0081] In further experiments it has been found in the comparative
brazing sheet product, that the application of a thin covering
material of aluminium having only 0.3% Fe and 0.5% Si slightly
improved the fillet formation to about 25%. This thin covering
material is in accordance with the teaching of prior art document
EP-1306207-B1.
[0082] Further experimental results showed that if no Mg is present
in the brazing sheet material (neither in the core layer nor in any
layer applied on top on the core layer) there is also no formation
of a fillet under controlled atmosphere condition when no brazing
flux is applied. Addition of a small amount of Mg in the second
Al--Si alloy clad layer in combination with a first Al--Si clad
layer material having no Mg addition further improves brazeability
under CAB condition without a brazing flux. However, the Mg content
in this second Al--Si alloy brazing clad material should not be too
high if one is to obtain a good fillet formation. Further improved
results are obtained when the second Al--Si alloy brazing clad
layer contains in combination Bi and Mg in the claimed range
together with a second Al--Si alloy brazing clad material layer. Bi
is added as one of the possible wetting agents. Good results are
obtained with Si levels of about 3% and of about 12% in the first
Al--Si alloy clad brazing layer.
[0083] Having now fully described the invention, it will be
apparent to one of ordinary skill in the art that many changes and
modifications can be made without departing from the spirit or
scope of the invention as herein described.
* * * * *